A vehicle powertrain typically includes a transmission, an engine, and a powertrain control module. The transmission transfers engine output torque through a gear reduction to a driveshaft, which rotates the wheels of the vehicle. The powertrain control module controls the operation of the transmission and the engine.
A clutch-to-clutch transmission combines two manual transmission autoshifts (MTAs). One MTA includes gears 1, 3, and 5 and the other MTA includes gears 2, 4, and 6. By combining two MTAs, a driver experiences less torque interruption during upshifts and downshifts.
A coast downshift under power (CDP) occurs when the transmission shifts from a higher gear (e.g., third gear) to a lower gear (e.g., second gear). For a given vehicle speed, a lower gear requires an increased engine speed as compared to a higher gear. In order to meet this increased engine speed requirement, two signals are automatically generated from the powertrain control module. One signal from the powertrain control module increases the throttle opening to deliver a maximum idle speed for the vehicle. This signal may be inadequate to deliver sufficient engine speed. Another signal generated from the powertrain control module commands a gear change. After shifting the gears, clutch-to-clutch torque occurs that increases the engine speed to allow the gears to be downshifted. Generally, the signal to increase the throttle opening remains active even though sufficient engine speed exists to attain a maximum idle speed for the vehicle. There are several disadvantages to this approach. Increasing the throttle opening increases fuel consumption. In addition, the combination of increased clutch-to-clutch torque and the signal to increase the throttle opening may result in slippage of the clutches between the two gears. Clutch slippage increases clutch wear. Moreover, the powertrain control module may need to rely more heavily on spark retard torque management.